Learn more about the common STI chlamydia.
Chlamydia is one of the most common sexually transmitted infections (STIs), with 1,515,985 reported cases in 2024. It’s caused by the bacterium Chlamydia trachomatis, which can be passed from one person with a chlamydia infection to their partner(s) through sexual contact such as vaginal, anal, or oral sex. It is not passed along through casual contact such as hugging or a shared toilet seat. Many people have chlamydia without knowing, so getting routinely tested if you’re sexually active is key.
Chlamydia bacteria are carried in semen, pre-cum, and vaginal fluids. This means it can be spread through sexual contact – most commonly, anal or vaginal sex, although it can also be passed through oral sex. It can infect mucous membranes such as the penis, vagina, cervix, anus, urethra, eyes, and throat. Importantly, the bacteria are not shared through contact such as hugging, kissing, holding hands, coughing, or sitting on the toilet.
Chlamydia can also be passed from a pregnant person to their baby during birth if the infection is present during pregnancy.
The most common symptom of many STIs, including chlamydia, are no symptoms at all. It’s estimated that up to 70-80% of people with vaginas and 50% of people with penises are asymptomatic (or don’t show symptoms) for chlamydia. This is what makes routine STI testing so important!
When symptoms are present, they often include:
If left untreated, even asymptomatic infections can cause disorders such as pelvic inflammatory disease (PID), or other long-term damage to the reproductive tract, including infertility.
Chlamydia is readily treatable with antibiotics. It’s important to follow the instructions given by your healthcare provider and to take the full course of treatment, otherwise it’s possible for the infection to remain or return.
It’s helpful to share your diagnosis with any sexual partner(s) so that they can also get treatment and avoid spreading the infection to others, or back-and-forth between yourself and your partner(s). Sometimes, you can get treatment for your partner(s) without them needing to be examined by a healthcare provider first, a practice called Expedited Partner Therapy (EPT).
The only way to completely avoid STIs like chlamydia is to avoid sexual contact. However, sex is a normal and healthy part of many people’s lives and there are steps you can take to lower your risk. Here are some ways to have safer sex:
A well-known antibiotic can help prevent infection, too! Doxycycline, also simply called doxy, is proving to be an effective preventative treatment when used correctly. If taken within 72 hours after sexual contact, doxy can help prevent chlamydia from becoming established in the body. This usage is called “doxy PEP.” So far, it’s only been proven to help in cisgender men and transgender women, but more studies are ongoing.
Please note that NCSD is not a medical facility. Content here is for informational purposes only and should not replace medical advice. Consult with a health care provider if you have questions or concerns regarding an STI.